Preformed and prestressed strap frame grid



14, 1965 F. H. GRIMONE 3,223,879

PREFQRMED AND PRESTRESSED STRAP FRAME GRID Filed Dec. 12. 1960 INVENTOR flank H Cir/mane BY y I WTORNEY United States Patent Cfifice 3,223,879 Patented Dec. 14, 1965 3,223,879 PREFORMED AND PRE TRESSED STRAP FRAME GRID Frank H. Grirnoue, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 12, 1960, Ser. No. 75,328 Claims. (Cl. 313348) The invention relates to grids of the type utilized in electron tubes to control the flow of electrons within the tube. In particular, the invention relates to frame grids, that is to say, to grids wherein the grid lateral supporting side members are held in spaced relationship by two or more structural portions which may either be cut from the same material as the side members in a die cut frame or may be attached cross-straps in a strap type frame.

One mode of attaching wires or grid laterals to a grid frame is by stretching individual wires across a frame and fastening the wires to the side members of the frame by notching and peening as shown in Patent No. 2,936,391 which issued on May 10, 1960 in the name of Gerald T. Curry and Stanley J. Gartner. Another method of manufacturing a frame grid is to wind grid lateral wire spirally about the frame, as in the Patent No. 2,507,709 which issued on May 16, 1950 in the name of Gronros as inventor.

In a flat stamped or die cut frame of the type disclosed in Curry and Gartner the tension on the grid may be maintained by making the sides of the frames as wide as desired or by adding strengthening reinforcing ribs to the frame, all of which requires a considerable amount of frame material. In the type of frame grid disclosed in Gronros, the side frame members are reinforced by concaving the metal of each half face of the grid frame in order to avoid inward bending and undesirable grid lateral sagging.

It is an object of this invention to minimize lateral grid wire sag in frame grids of the type using relatively light and resilient side frame members.

Briefly in one aspect of the invention, I provide a grid frame having resilient outwardly bowed side members which are substantially straightened out during the grid winding process and as a result continuously maintain tension on the lateral grid wires.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 shows a strap frame grid of the invention, with bowing of the side rods exaggerated to better show one aspect of the invention;

FIG. 2 is an end view of the frame; and

FIG. 3 is a view of the wound grid.

The grid frame is comprised of two resilient side rods 14 and 16 which are of any of various cross-sections. Thus they may be circular, square or rectangular in crosssection. In the specific example shown, the rods are shown as of circular cross-section. The side rods 10 are held in desired spaced relationship to each other by pairs of cross straps 18 and 20 welded or otherwise firmly secured thereto.

The side rods 10, it will be noted, are prestressed to present bowed portions 22 between the straps 18 and 20, the bowing being outward of the frame, while the leg portions 24 of the side rods external straps 18 and 20 are unstressed and parallel to each other.

The grid laterals 12 are wound in conventional manner about the frame, being fastened to the side rods by known methods such as welding or notching and peening at the lateral wire ends A and B. The frame prior to being wire wound is slid onto a mandrel against which all of the leg portions 24 lie snugly, with the bowed portions extending away from the mandrel. The wire, in accordance with conventional practice, is wound spirally about the grid frame with the wire fed to the grid frame under tension. As the grid frame is wound, the tension on the wire brings the bowed portions of the frame into contact with the mandrel, resulting in the wound grid of FIG. 3, wherein the side rods are parallel to each other throughout their length and the grid laterals are under tension. In the winding operation, the wire, under tension, progressively pulls the bowed portions of the side rods toward the mandrel in a manner such that none of the previously wound turns tend to become loose. Preferably, only the end turns are secured to the side rods to allow for equalization of tension in the grid laterals, though notching may be employed to position the turns.

Due to the prestressing of the side rods, even when the grid laterals are heated, as in use within an electron tube, the side rods though tending to return to the bowed condition, will still maintain the wires taut.

The bowing is shown in an exaggerated degree in FIGS. 1 and 2. In actual practice where a grid lateral wire .0003 inchin diameter is wound with conventional tension about the strap frame grid with 750 turns per inch, the bowing of each side rod would be, at the maximum diameter of the frame, from .004 inch to .005 inch from the straight line condition of the side rod. However, these dimensions may be varied to some extent depending, amongst other factors, on the amount of prestressing of the side rods, the diameter of the grid lateral wire, the tension on the wire and the number of turns per inch.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What I claim is:

1. A frame for a grid comprising resilient side members and cross members, the side members having portions bowed away from each other between the cross members and each of the side members extending beyond each of the cross members to form spaced parallel leg portions for support of said frame.

2. A frame for a grid comprising resilient side members and cross members, the side members having portions bowed away from each other between the cross members and each of the side members extending beyond each of the cross members to form parallel leg portions, each of the cross members comprising a pair of straps, one on each side of and welded to the side members.

3. A frame grid comprising a frame having parallel resilient side rods and cross members near the ends of the rods integrally fastened to the side rods and a wire under tension spirally wound about the side rods, the side rods being stressed to a condition where, between the cross members, they tend to bow away from each other.

4. A frame grid comprising a frame having parallel resilient side rods and cross members near the ends of the rods integrally fastened to the side rods and a wire under tension spirally wound about the side rods, the side rods being stressed to a condition where, between the cross members, they tend to bow away from each other, each of said cross members comprising a pair of straps welded to opposite sides of the side rods, the ends of the side rods beyond the cross members forming leg portions parallel to each other.

5. In a frame for supporting a helix of lateral grid wires the combination comprising two side members supported in a common plane by upper and lower cross straps to define an internal grid Window having a length equal to the distance between the cross straps, said side members being formed to extend in parallel spaced relationship external the grid Window and to bow symmetrically away from each other through the grid window length with a maximum spacing greater than said spaced relationship substantially midway between said cross straps along the length of the grid window.

References Cited by the Examiner UNITED STATES PATENTS 1,657,221 1/1928 Metcalf et a1 313348 X 1,984,993 12/1934 Ronci et al 313-285 2,495,259 1/1950 Jackson 313350 X 2,624,100 1/1953 Foulkes 313-348 X FOREIGN PATENTS 1,231,582 9/1960 France. 1,093,915 12/1960 Germany.

770,817 3/1957 Great Britain.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, ARTHUR GAUSS, ROBERT SEGAL, Examiners. 

1. A FRAME FOR A GRID COMPRISING RESILIENT SIDE MEMBERS AND CROSS MEMBERS, THE SIDE MEMBERS HAVING PORTIONS BOWED AWAY FROM EACH OTHER BETWEEN THE CROSS MEMBERS AND EACH OF THE SIDE MEMBERS EXTENDING BEYOND EACH OF THE CROSS MEMBERS TO FORM SPACED PARALLEL LEG PORTIONS FOR SUPPORT OF SAID FRAME. 